Adjacent slabs of concrete are commonly connected by dowel bars, the ends of which are inserted in the side edge of a freshly poured strethc of concrete. The other extending ends of the dowels become embedded in the adjacent slap of concrete when it is poured. When the concrete sets, the adjacent portions, although poured at different times, are firmly bound together assuming the bars are properly spaced apart. In one particular job, where runways at an airport were being laid, the dowels were twenty inches long, with half the length in each of the adjacent concrete slabs. The dowels were inserted in the middle of the thickness of the slab. The dowels were one and a quarter inches in diameter and spaced about 15 inches apart. The concrete has to be very stiff to prevent the dowels from sagging prior to setting of the concrete. Once the concrete has set, the dowels remain in fixed position when the adjacent lane is poured.
It is an object of the present invention to mechanize the insertion of the dowels while confining the top and side surfaces of the slab during this operation and preventing the side retaining plates from digging into the slab should the course of the slab deviate from a straight direction.
It is common practice to establish concrete pavement slabs by using slipform pavers. These are self propelled machines having spaced vertical side forms and a screed sometimes called an extrusion meter extending between the side forms. The extrusion meter is supported by the frame and screeds the concrete deposited on the road bed ahead of the advancing machine. The pressure exerted by the side forms and the extrusion meter is sufficient so that the contour of the slab is retained as the machine moves ahead and loses contact therewith. It is into such a slab that the dowels are inserted. When an adjoining slab is formcd, one side of the slipform paver is elevated and runs on the original slab which has now firmly set, while the other side of the paver travels on the prepared grade. The two slabs are firmly connected by the embedded dowel bars.